The present embodiments relate to methods and systems for connecting an offshore first electrical plant, which is a wind turbine generator, to a second electrical plant. The present embodiments also relate to electrical connectors for connecting a cable to an offshore electrical plant such as a wind turbine generator.
It is known to provide offshore wind farms including multiple wind turbine generators. A typical farm will include multiple renewable wind turbine generators connected in a daisy chain manner, by inter-array cables, to an electrical sub-station, where the generated power is collected, processed, and fed back to a station onshore. The power is generated at low voltage and stepped up for transmission back to the sub-station, which may either be onshore or offshore.
Typically, each wind turbine generator has two cables, one into the generator and one out, which allows the wind farm to be connected up in the daisy chain arrangement and allows the wind turbine generator at the end of the chain to be connected to the sub-station. The cables between the energy generators and also the cable between one of the energy generators and the sub-station are known as inter-array cables or infield cables.
A known method for installing a wind farm involves installing the wind turbine generator support structures, typically about 1 km apart and laying inter-array cables between the support structures. The inter-array cables are laid, and a plough is used to create a furrow in which the inter-array cable sits and is covered over (e.g., buried in the seabed).
The generator support structures are provided with a feature to allow the end of an inter-array cable to be pulled from the seabed to a part of the structure that is above the water line. This feature may be in the form of a tube, either internal or external to the support structure that the cable may be pulled through. Alternatively, this feature may be an aperture in the support structure that allows the cable to be pulled up through the support structure itself. Typically these features have a mouth at the bottom end, near the sea bed, for receiving the end of an inter-array cable and a bend to direct the cable round to the vertical and allow the cable to extend upwardly to above the surface. Due to the typical shape of this feature, it is commonly known as a ‘J-tube’. However, other shapes and types of feature are also used, which are also generically referred to as the “J-tube” (e.g., a feature that allows the cable to be pulled from the seabed up through the structure is generically termed a “J-tube”), whatever its specific design.
When it is desired to connect the inter-array cable to the wind turbine generator, a lifting wire is passed downwardly from the structure above the surface through the J-tube to a bottom end. Alternatively, the lifting wire may have been pre-installed in the J-tube onshore. The lifting wire is attached to the end of the inter-array cable and is then winched up the J-tube, thereby pulling the inter-array cable through the J-tube for connection to the wind turbine generator. The attachment of the lifting wire to the inter-array cable on the seabed is carried out by underwater operatives or remotely operated vehicles (ROVs).
Once the inter-array cable has been winched up through the J-tube, steel armor wires in the cable are clamped or terminated to the structure, thus mechanically anchoring the cable to the structure. Rocks are placed around the bottom of the support structure to provide scour protection to protect the inter-array cable and to prevent the support structure being eroded by eddy currents.
Another team of operatives on the tower connects the internal parts (e.g., copper wire and fiber optics) of the inter-array cable to the renewable energy generator.